This invention relates to an access point, acting as a basestation in a cellular wireless communications network, and in particular to such an access point, in which maximum transmit power levels of the access point are controlled in such a way as to avoid interference while ensuring acceptable coverage.
In conventional cellular networks, basestations are installed by the network operators, in order to provide coverage for the areas where the network operators expect there to be a demand for their services. The network planners are able to choose the locations of the basestations, and are able to set the maximum transmit powers, of the basestation itself and of the mobile devices that establish connections with the basestation, in order to ensure a certain coverage and Quality of Service (QoS). To achieve these aims, the process requires detailed site surveys and geographical planning. When a maximum transmit power has been set, this effectively sets the size of the cell served by the basestation, because it determines the range over which the transmissions from the basestation can successfully be received. The maximum transmit power is rarely changed after it has initially been set, but can be altered from the network if necessary, for example because of changes to the radio network.
When a maximum transmit power has been set for the basestation, and calls are in progress, power control is also applied to the transmissions within these calls. Firstly, an initial transmit power is set, for example based on the power of a received access request, and thereafter power control is applied to the transmissions, based on signal strength measurements made by the mobile device involved in the call and reported back to the basestation. Such power control can operate very quickly. For example, the power level used by a basestation for its transmissions can be adapted at a frequency in the kilohertz region. That is, the power level can in theory change many times per second if the signal strength measurements indicate this.
In the case of access points (also known as femtocell basestations), these are intended to be available for purchase by consumers themselves for location within a home or office, and are intended to provide cellular coverage over relatively small geographical areas, for example only within the building in which they are located. For such devices, costly site surveys and detailed radio network planning are not possible. It is therefore proposed that such devices should be able to configure themselves, based on the local radio environment.
U.S. Pat. No. 6,314,294 relates to a basestation, in which RF transmit power levels are self calibrated, using data collected by the wireless system.